1. Field of the Invention
The present invention relates in general to radiation detectors and more specifically to such detectors that have a directional screen.
2. Description of the Prior Art
There are a number of radiation detectors presently known in the art but the operation of such known detectors is hinged upon the use of a small area sensing medium such as a crystal. Because of the small size of the sensing medium of such known detectors, sufficient radiation exposure of the sensing medium is difficult to achieve without resorting to special equipment. For example, to increase the amount of radiation exposure of the sensing medium often small area detectors include a lens or spherical mirror to focus a large amount of radiation on the sensing medium. Although such focusing means has proved operationally satisfactory, the use of a focusing lens or spherical mirror is relatively expensive and adds considerably to the price of a detector. To avoid the need of a focusing means, the present invention employs a large area sensing medium in the form of a layer of pyroelectric material. However, one problem with the use of a detector with a large area sensing medium is that the directionality of the detector is significantly reduced and, consequently, the field of view of the detector is too large for many purposes.
Various types of shields or screens for providing a directional capability are known in the art as evidenced by U.S. Pat. Nos, 3,821,463; 3,546,359; 3,584,134; and 3,231,663. However, such patents do not disclose the use of such shields or screens for providing a detector with directional capabilities and in spite of such art the need still exists for a directional radiation detector that is of a convenient size for portable use and yet is relatively inexpensive and simplistic in construction.